Device for preventing cable damage during installation

ABSTRACT

A device to prevent cables from becoming damaged during the installation process is disclosed. The tolerances that a particular cable can withstand will typically vary dependent upon the type of cable and the number of cables pulled together. A magnetic linkage is therefore disposed between the cable and a pulling rope or cable and is adapted to break when a force appropriate to the particular installation scenario is applied (i.e. a force within the tolerance level specified by the manufacturer).

[0001] The present invention relates to the installation of cabling, andmore specifically to a device for preventing cable damage duringinstallation.

[0002] Twisted pair copper cabling has traditionally been used to carryvoice and data to end-users and typically hundreds of metres of cablinghas to be run above ceiling or underground to reach those users.Potential damage to the cables during the installation process is a bigproblem since if too great a force is exerted on these cables then thetwisted pair conductors inside the cabling insulating sheath are overstretched. Consequently the distance between the twisted pairs will bereduced giving rise to an increase in cross-talk and reducing theeffectiveness of the cables. Further one or more of the conductors mayeven break.

[0003] Installers typically pull these cables in from 500 m drums. Iffor example offices require four voice/data connection points, theninstallers will in all likelihood pull from four drums at a time. Thusthey are in fact attempting to pull 2 km of cable from a standing start.This is where damage is likely to occur.

[0004] The onset of Cat 6/7 standards has placed demands onmanufacturers for even greater performance and bandwidth. Cabling suchShielded Foiled Twisted Pair (SFTP) has been developed to meet theseincreased demands. With such cabling, each twisted pair conductor issurrounded by a layer of aluminium foil. All the pairs are then coveredby a further layer of foil and then a braided shield of wires. This newconfiguration permits an information transfer rate of approximately 200Gigabytes per second as opposed to the 100 Megabytes per second providedby the basic twisted pair cabling. However such a transfer rate is evenmore highly dependent upon the precise positioning of the twisted pairconductors within the cabling sheath.

[0005] Such copper cables typically cannot retain their configuration ifstressed (pulled) beyond SON (5 Kg). The cable manufacturers clearlydefine the tolerances that their products can withstand and these aretypically:

[0006] 1×4 pair cable pulled in by hand SON (5 Kg)

[0007] 2×4 pair cables pulled in by hand 75N

[0008] 3×4 pairs cables pulled in by hand 100N

[0009] X×4 pair cables pulled in by hand X×25+25N (up to a maximum of200N)

[0010] Installing such cabling can prove extremely time consuming. Sinceit will not be visibly obvious that a cable has been over stressed, aninstaller will typically complete an installation and only discover thatthe cable has become damaged when performing tests subsequently. Theywill then have to start the process all over again, having wasted manyhours. The damaged cabling will also have to be replaced and this canprove costly. Sophisticated cabling such as SFTP currently retails atapproximately £185 a reel.

[0011] The installation process has proved problematic for many yearsand not just with the copper cabling. When fibre cables first started toappear, this issue was resolved by the introduction of pulling fusessuch as the type manufactured by Condux International, Inc. Such adevice is attached between the cable being pulled and a pulling rope orcable. It typically consists of two barrels linked together by aninternal metal break pin. The metal pin is precisely manufactured tobreak when the desired amount of stress or tension is exerted on thecable being pulled, thus preventing internal damage to the cable.Different metal pins are available dependent upon the break pointrequired.

[0012] Unfortunately it is not possible to use such devices effectivelywhen installing fragile SFTP copper cabling. Fibre optic cabling is farstronger, and so all these devices are made up of physical barrels whichwill typically snap in half at between 667 and 8,006 N. This is far toohigh a figure for the copper cable application and it is currently notpossible to manufacture metal pins which break under the much reducedamount of strain required. This is because the thinner the metal pin ismade, the more difficult it becomes to control the break point.

[0013] Accordingly, the invention provides a magnetic linkage for cableinstallation, the linkage comprising: two components, which in operationare held together by magnetic attraction, one of the components beingadapted to attach, via first attachment means, to the cable and theother component being adapted to attach, via second attachment means, toa pulling rope, the components further being adapted to break apart whena predetermined pulling force is applied.

[0014] As stated above, the type of cables to which the invention isparticularly applicable can be extremely fragile because the precisepositioning of the conductors within the cabling sheath is typicallyimportant. If the cables are over stretched (i.e. the predeterminedforce is exceeded), then the cables are likely to become damaged. Thelinkage or cable pull of the present invention decouples when thepredetermined force is applied and breaks the pulling tension. The cableinstaller is warned by the sudden reduction in the pulling tension thatthey were dangerously close to damaging the cable, but no actual damageis done. The installer is able to quickly and easily reset the linkageand continue with the installation. Such a linkage saves time becausepreviously only subsequent installation tests would determine that therewas a problem with the cable. (The damage is typically not visible butis contained within the cabling sheath.) Further such cables areexpensive and this linkage therefore represents a huge cost saving bybreaking before the cables are themselves damaged.

[0015] In a preferred embodiment the first component comprises amagnetic portion and the second component comprises a magneticallyattractable portion. The magnetic portion comprises a permanent magnethaving a strength that will remain constant over the lifetime of thelinkage (unless it is recalibrated). The magnetically attractableportion comprises a material which is attracted by the magnet (e.g. aferrous material such as iron). It will of course be appreciated thatalternatively two components each with magnetic portions could be used.

[0016] In a preferred embodiment the magnetically attractable portion ofthe second component has a controlled contact area with the magneticportion of the first component. This contact area is used to control theamount of force required to break the magnetic linkage. It will beappreciated that it is also possible for the force required to break thelinkage to be set by controlling the strength of the magnetic portion ofthe first component (or by a combination of both methods). However, itis easier in practice to machine the magnetically attractable portion ofthe first component so that a particular configuration of the contactarea determines the load under which the two components decouple. Thecalibration provided is in this way much more precise. One convenientway is to configure the surface profile of the magnetically attractableportion of the second component to provide the controlled contact areawith the magnetic portion of the first component. It is also possible tomachine the magnetic portion to control the contact area with themagnetically attractable portion but this is not as straightforward amethod because the magnet may be less easy to machine, and changes inthe shape of the magnet affect both the contact area and field strength.

[0017] In a preferred embodiment the first component has a maleconnector which is inserted into a female connector on the secondcomponent to provide the linkage (although the male and femalecomponents could of course be reversed). The female connector ispreferably a sheath of circular cross-section which makes insertion ofthe male connector easier by avoiding the need for any rotationalalignment when forming the linkage. However a wide variety of othershapes and configurations could also be used.

[0018] The male connector is preferably sized to fit snugly inside thefemale connector. It will be appreciated that without this snug fit, itwould be possible for the two components to get separated from oneanother during the installation process by a bending force that wouldtend to snap the linkage sideways, rather than pulling it apart. Thesheath therefore holds the components in position regardless of anysideways forces exerted on the linkage. This ensures that the linkage isonly broken by a force exerted in a direction parallel to the directionin which the cable is being pulled. The flush fit between the first andsecond components also makes it possible to reproduce the position inwhich the two components couple to one another. This in turn ensuresthat a consistent breaking force is required to separate the linkage.

[0019] In a preferred embodiment, the interior of the female connectorhas a rim and in use the male connector is inserted into the femaleconnector until it abuts that rim. This precise positioning again helpsto ensure a consistent linkage force. The rim has a contact area whichis controlled in accordance with the desired predetermined force. Themore material that makes contact with the magnetic portion of the firstcomponent the greater the force that is required to break the linkage.In one embodiment the rim comprises a plurality of crenellations, whichprovide a convenient way of controlling the contact area by adjustingthe spacing of the crenellations.

[0020] Preferably, the first and/or second attachment means each includea swivel piece. This allows for rotation of the linkage relative to thecable axis during the pulling process, thereby preventing the cable frombecoming twisted during installation. Preferably the first and/or secondattachment means includes a pivotable loop onto which the cable orpulling rope (as appropriate) can be fastened. This provides flexibilityand reduces the risk of bending damage to the cable.

[0021] It will be appreciated that the tolerances that a particularcable can withstand will typically vary dependent upon the type of cableand the number of cables pulled together. Examples of these toleranceshave been given in the background section. Therefore one of the twocomponents of the magnetic linkage preferably includes a detachablesub-component to allow replacement by another sub-component thatprovides a magnetic attraction of different strength between the twocomponents.

[0022] In one preferred embodiment, the magnetic linkage is suppliedwith a set of sub-components that are interchangeable into the linkage.Each sub-component is calibrated to provide a different predeterminedbreaking force. For example, the linkage can be supplied with a kit ofthree different sub-components, one for each of the cabling loadsmentioned in the background section. Thus by way of example, there isone sub-component where the predetermined force is 50N; one for 75N andone for 100N (note, the predetermined force is preferably not more than200N). It will be appreciated that the invention is not limited to theseprecise specifications and that any number of sub-components arepossible. Because one sub-component may be substituted for another, itis possible for the linkage to be used in differing installationscenarios and also to keep pace with new developments in the cablingindustry. For example, if a new and more fragile cable becomes availableit will be possible to manufacture a sub-component which will decouplefrom the second component under a suitably low strain.

[0023] A preferred embodiment of the present invention will now bedescribed, by way of example only, and with reference to the followingdrawings:

[0024]FIGS. 1 and 2 show the device of the present invention at twostages of operation in accordance with a preferred embodiment; and

[0025]FIGS. 3a and 3 b show the interior of the magnetically attractablecomponent of the present invention in accordance with two preferredembodiments.

[0026] As shown in FIG. 1, a device has been designed having twoprincipal components: an open-ended steel barrel housing a magnet(magnetic component 10); and a magnetically attractable component 20. Inuse the two components are held together by the magnetic force of themagnetic component. The magnetic component is attachable to a rope usedfor pulling 30 the cable, which is being installed, via a swivel piece50 and a loop 40. The magnetically attractable component is attachableto the cable itself 60 via swivel piece 80 and a loop 70. Typically thecable is placed inside a metal grip 90 which tightens around the cableto hold it securely in place. It is the metal grip which is actuallyattached to loop 70. The swivel pieces are incorporated to allow formovement of the cable during the pulling process, thereby preventing itfrom becoming twisted during installation.

[0027] The magnetically attractable component has been preciselymachined such that placing the two principal components under a desiredamount of strain during installation will cause them to separate,thereby releasing the tension on the cable before it becomes overstressed and damaged (see FIG. 2). When the two components part, thetension is broken making the installers quickly aware that they wereexerting too great a force on the cable.

[0028] Unlike the pulling fuses of the prior art it is possible toensure that the magnetic force holding the two components together isbroken under the comparatively low pulling loads listed in thebackground section. The device is not dependent upon consumables such asreplacement broken metal pins and has few moving parts which are likelyto require substitution. It is consequently extremely robust. The devicetherefore typically represents a one off cost to the installer. Further,the loops and swivel pieces are preferably made out of a lightweightmaterial such as aluminium and the two principle components are alsorelatively lightweight. It is therefore possible to manufacture such adevice weighing under 200 grammes in total. This is advantageous becauseit means that it cannot damage the cables when it operates (i.e. if itfalls on the cables when the magnetic contact is broken).

[0029]FIGS. 3a and 3 b show the machined interior of two magneticallyattractable components, each one designed to decouple from the magneticcomponent when placed under a different level of stress. Themagnetically attractable component has an outer casing or sheath loowhich houses a smaller barrel 110 with a rim 120, 125. The amount andthickness of the material making up the rim is precisely manufactured todetermine the force under which the magnetic component and themagnetically attractable component will separate. The more material thatmakes contact with the magnetic component the greater the force thatwill be required. In FIG. 3 a the rim 120 has a crenelated profile (thecrenellations being shaded and the gaps between the crenellations shownin white). FIG. 3b shows a complete rim 125 with no gaps and thusrequires a greater force in operation before the two components willdecouple than the magnetically attractable component shown in FIG. 3a.This is because in FIG. 3b the surface area of the rim which actuallymakes contact with the magnetic component is greater than in FIG. 3a.Thus the thickness of the rim also is a determining factor.

[0030] Apart from precise machining, it is preferable to ensure that themagnetic component makes a flush fit with the rim of the magneticallyattractable component. This is made possible by the outer casing whichenables the reproduction of the position in which the two componentscouple to one another. This in turn ensures that a consistent breakingforce is required to separate the magnetic linkage. Further, it will beappreciated that without snug fit possible due to the casing surroundingthe interior barrel of the magnetically attractable component, the twocomponents could get separated from one another during the installationprocess by a bending force that would tend to snap the magnetic linkagesideways, rather than pulling it apart. The casing therefore holds thecomponents in position regardless of any sideways forces exerted on thelinkage. This ensures that the linkage is only broken by a force exertedin a direction parallel to the direction in which the cable is beingpulled. Of course if the magnetic coupling is broken under a loadlighter than is desirable, it is not damaging to the cable but isfrustrating for the installers who continually have to reset the device.

[0031] It should also be noted that the surface of the magneticcomponent which makes contact with the magnetically attractablecomponent should be as free from contamination as is possible. This isbecause any contaminants are also likely to cause the two components tobreak contact with one another earlier than is desirable.

[0032] Preferably the device is stored as is shown in FIG. 1 with thetwo components in contact with one another. This should preventcontamination of the magnetic component. However, should the componentbecome contaminated then the surface of the magnetic component whichmakes contact with the magnetically attractable component can simply bewiped clean.

[0033] A further advantages of the preferred embodiment is that theswivel pieces of the device 50, 80 allow their respective component tomove with the pulling rope/cable. Moreover, the coupling device verycompact and is unlikely to catch on anything during the installationprocess.

[0034] To allow the device to be used with different magneticallyattractable components and thereby be resistant to different amounts ofstrain, the magnetically attractable component has an aperture 130 forreceiving a threaded screw of swivel piece 80. It is therefore possibleto unscrew one magnetically attractable component and replace it withanother. In one embodiment the device is supplied with a kit of threedifferent magnetically attractable components. There is one magneticallyattractable component for each of the cabling loads mentioned in thebackground section. It will be appreciated that the invention is notlimited to such and that any number of magnetically attractablecomponents are possible. Because one magnetically attractable componentmay be substituted for another, it is possible for the device to be usedin differing installation scenarios and also to keep pace with newdevelopments in the cabling industry. For example, if a new and morefragile cable becomes available it will be possible to manufacture amagnetically attractable component which will part company with amagnetic component under a suitably low strain.

[0035] It will be appreciated that whilst the invention has beendescribed primarily in terms of interchangeable magnetically attractablecomponents, it would be possible for the device to use interchangeablemagnetic components. With such an alternative design, the strength ofthe magnetic component is precisely controlled to set the force requiredto separate the two components. However, it is easier to machine themagnetically attractable component such that a particular configurationof the area which makes contact with the magnetic component controls theload under which the two components separate. The control provided is inthis way more precise.

[0036] Further whilst the invention has been described in terms of itsapplicability to SFTP copper cabling, it will be appreciated that theinvention is applicable to any type of cabling. As has been described,it is however particularly suitable for protecting fragile cabling sinceit is possible to cause the magnetic component and the magneticallyattractable component to separate from one another under a much lowerstrain than the prior art devices.

1-11. (canceled)
 12. A magnetic linkage for cable installation,comprising: first and second components, which in operation are heldtogether by magnetic attraction, one of the first and second componentsbeing adapted to attach, via first attachment means, to a cable and theother of the first and second components being adapted to attach, viasecond attachment means, to a pulling rope, the first and secondcomponents further being adapted to break apart when a predeterminedpulling force is applied.
 13. The magnetic linkage of claim 1, whereinthe first component comprises a magnetic portion and the secondcomponent comprises a magnetically attractable portion.
 14. The magneticlinkage of claim 2, wherein the magnetically attractable portion of thesecond component has a controlled contact area with the magnetic portionof the first component.
 15. The magnetic linkage of claim 3, wherein asurface profile of the magnetically attractable portion of the secondcomponent is configured to provide the controlled contact area with themagnetic portion of the first component.
 16. The magnetic linkage ofclaim 1, wherein the first component has a male connector that isinserted into a female connector on the second component to provide saidlinkage.
 17. The magnetic linkage of claim 5 wherein the femaleconnector is a sheath of circular cross-section, the male connectorbeing sized to fit snugly therein.
 18. The magnetic linkage of claim 5,wherein the interior of the female connector has a rim and in use themale connector is inserted into the female connector until it abuts saidrim.
 19. The magnetic linkage of claim 6, wherein the interior of thefemale connector has a rim and in use the male connector is insertedinto the female connector until it abuts said rim.
 20. The magneticlinkage of claim 7, wherein said rim has a controlled contact areadependent on said predetermined force.
 21. The magnetic linkage of claim1, wherein the first attachment means includes a swivel piece.
 22. Themagnetic linkage of claim 1, wherein the second attachment meansincludes a swivel piece.
 23. The magnetic linkage of claim 1, whereinthe first attachment means includes a pivotable loop.
 24. The magneticlinkage of claim 1, wherein the second attachment means includes apivotable loop.
 25. The magnetic linkage of claim 1, wherein one of thefirst and second components includes a detachable sub-component to allowreplacement by another sub-component that results in a magneticattraction of different strength between the first and secondcomponents.